Technical Abstract:
Two snap bean cultivars, Strike and Carlos (Phaseolus vulgaris, L), were planted into a Hebbronville sandy loam soil on 22 Feb. 2000 and grown under 0, 30, and 70 of ambient daily light (shade) throughout the 65-day growing season. Although the yield response was linear with respect to increased shading, first harvest and season yields were not affected by a 30% incident light reduction. Light reduction tended to decrease the larger pod sieve sizes, but increased pod dry matter content in 'Carlos'. Plant biomass was reduced by shading, as was leaf greenness, but leaf area and chlorophyll content (dry wt. basis), as well as the incidence of powdery mildew late in the season, was increased by shading. Leaf, air, and soil (at 10 cm) temperatures were reduced by increased shading. The incidence of powdery mildew occurred late in the season and was linearly increased by reduced light. Leaf transpiration and stomatal conductance was generally increased by shading. Rhizobium nodulation of 'Carlos' roots was greater under reduced light. Pod mineral nutrients varied between cultivars, but generally were not affected by light intensity.